The invention pertains to bipolar transistor constructions, and to methods of forming bipolar transistor constructions.
Bipolar transistor constructions can have numerous applications in modern semiconductor devices. For instance, bipolar transistors can be incorporated into electrostatic discharge (ESD) protection schemes for complementary metal oxide semiconductor (CMOS) assemblies. An exemplary CMOS assembly is described with reference to FIG. 1, which illustrates a fragment of a semiconductor wafer 10.
Wafer 10 comprises a substrate 12. Substrate 12 can comprise, consist essentially of, or consist of monocrystalline silicon lightly doped with a background p-type dopant (so-called p-minus, or pxe2x88x92, doping). To aid in interpretation of the claims that follow, the terms xe2x80x9csemiconductive substratexe2x80x9d and xe2x80x9csemiconductor substratexe2x80x9d are defined to mean any construction comprising semiconductive material, including, but not limited to, bulk semiconductive materials such as a semiconductive wafer (either alone or in assemblies comprising other materials thereon), and semiconductive material layers (either alone or in assemblies comprising other materials). The term xe2x80x9csubstratexe2x80x9d refers to any supporting structure, including, but not limited to, the semiconductive substrates described above.
An exemplary background p-type dopant concentration within substrate 12 is less than 1xc3x971016 atoms/cm3; such as, for example, from about 1xc3x971014 atoms/cm3 to about 1xc3x971016 atoms/cm3. A suitable p-type dopant is boron.
A plurality of n-wells 14, 16 and 18 are formed within substrate 12 by implanting a suitable n-type dopant (such as, for example, phosphorous or arsenic) into substrate 12. The concentration of n-type dopant within n-wells 14, 16 and 18 is preferably at least 10-fold higher than the background concentration of p-type dopant within substrate 12, and accordingly overwhelms the p-type dopant within regions 14, 16 and 18. A suitable concentration of n-type dopant is from about 1xc3x971015 atoms/cm3 to about 1xc3x971018 atoms/cm3.
A plurality of isolation regions 20 are formed across an upper surface of substrate 12. Isolation regions 20 can comprise, for example, shallow trench isolation regions filled with an appropriate insulative material, such as silicon dioxide.
A plurality of p-type metal oxide semiconductor (PMOS) transistor structures 22 are formed to be supported by substrate 12, and to be associated with n-well regions 14, 16 and 18. Also, a plurality of n-type metal oxide semiconductor (NMOS) transistor constructions 24 are formed to extend across substrate 12 and to be associated with p-type regions between the n-wells. PMOS transistors 22 comprise source/drain regions 26 which are doped with an appropriate p-type dopant, and NMOS transistors 24 comprise source/drain regions 28 which are doped with an appropriate n-type dopant. NMOS transistors 22 and PMOS transistors 24 comprise transistor gate structures 30 and sidewall spacers 32 along the transistor gates. Transistor gates 30 can comprise, for example, a layer of gate oxide and overlying layers of conductive materials (such as, for example, one or more of conductively-doped silicon, metal and metal silicide). Sidewalls 32 can comprise, for example, silicon nitride or silicon dioxide. The transistor gates associated with NMOS constructions 24 can be different than those associated with PMOS constructions 22. For instance, the gates associated with the NMOS constructions can comprise n-type conductively doped polycrystalline silicon, while the gates associated with the PMOS constructions can comprise p-type conductively doped polycrystalline silicon.
It would be desirable to develop bipolar transistor constructions which can be readily incorporated into CMOS assemblies of the type described with reference to FIG. 1.
In one aspect, the invention encompasses a bipolar transistor construction having a collector region, emitter region, and base region extending within a semiconductive material substrate. The construction further comprises separate access regions associated with the base region, emitter region and collector region, respectively. An n-type doped connecting region is comprised by the collector region and extends beneath the emitter and base regions. A p-type doped location is comprised by the base region and extends beneath the emitter region and above the n-type doped connecting region. An n-type doped intermediate location is within the emitter region and between the p-type doped location and the emitter access region.
In other aspects, the invention encompasses methods of forming bipolar transistor constructions.